cos^2x/2-sin^2x/2-sinx
=cosx-sinx
=√2(√2/2cosx-√2/2sinx)
=√2(sinπ/4cosx-cosπ/4sinx）
=√2sin(π/4-x)
T=|2π/w|
=|2π/(-1)|
=|-2π|=2π